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Xil. Cathode Rays and some Analogous Rays. 
By SiLVANUS P. Thompson, D.Sc., F.R.S. 
Received May 10,—Read June 17, 1897. 
1. On the Electrostatic Dejiection of Cathode Rays and the Production of Negative 
Cathodic Shadows. 
In the experiments first to be described, the aim of the research was primarily to 
discover whether, and in what way, the shadow cast by the so-called cathode ray^ 
was affected by the physical state of the object interposed between the cathode and 
the tube-wall, or other opposing surface capable of luminescing under the stimulation 
of the ray. 
A pear-shaped Crookes tube, depicted in fig. 1, was made, having as an electrode 
at its smaller end a flat disk. A, of aluminium. At opposite sides of the bulb were 
introduced transversely two short cylindrical electrodes, B and C, of aluminium 
wire. These were mounted, as usual, on platinum wires, which were fused into the 
aluminium and sealed in through the glass wall of the tube. This tube was 
exhausted until the stage was reached at which all the pale internal nebuloid 
patches of luminous gas had disappeared, and the tube showed the yellow-green 
surface luminescence characteristic of soda-glass. When A was used as cathode, 
Rontgen rays were emitted from the glass at the opposite end of the tube, but the 
exhaustion was only just sufficient for this purpose, the emission ceasing when the 
tube became warmed with prolonged discharges. At this particular stage of 
exhaustion the tube was sealed off. It was in that stage of exhaustion in which it 
exhibited, in the luminous patch opposite the cathode, a singular unstable creeping 
luminosity, flickering in dendritic forms suggestive to the casual observer of splashes. 
The phenomenon has frequently been observed in Rontgen tubes, and is the subject 
of further notice in | 3 below. Throughout the entire research the electric source 
employed was an Aprs induction coil capable of yielding sparks 25 centims. long, 
but with the break ordinarily adjusted so as to yield sparks up to 8 or 10 centims. 
only in length. 
When the flat electrode. A, of this tube was made the cathode, shadows of B and 
* The term ray is used here and throughout in the most general sense, not as in any way postulating 
a wave-propagation. 
8.3.98 
